Generally, ceramic-based honeycomb structures are produced through a procedure of, for example, molding (e.g., extruding) a raw material composition containing a predetermined ceramic source and water to thereby form a honeycomb formed body having a plurality of cells defined by partition walls, each cell serving as a fluid conduit; drying the honeycomb formed body; and firing the dried honeycomb formed body.
Among the above production steps for a ceramic honeycomb structure, drying of a honeycomb formed body is carried out by means of, for example, hot air or high-frequency heating employing an electromagnetic wave. In electromagnetic wave drying, an electromagnetic wave of high-frequency region (high-frequency wave) capable of heating water is applied to a honeycomb formed body, whereby water is vaporized so as to dry the honeycomb formed body (see, for example, Patent Document 1). As compared with drying with hot air, electromagnetic wave drying more effectively dries from an inner part of a honeycomb formed body. However, in this case, the outer part of the formed body is difficult to dry as compared with the inner part, which is problematic.
In addition, when a honeycomb formed body has a thin outer wall or partition walls, drying by means of high-frequency heating employing an electromagnetic wave raises a problem. Specifically, due to the structural nature, the outer part of the thus-dried formed body is not readily dried as compared with the inner part thereof, wrinkles and dents generate in the outer periphery, whereby warpage of partition walls, and other deformation are problematically generated. The characteristic feature of the method for drying a honeycomb formed body described in Patent Document 1 is that the humidity of an atmosphere including a honeycomb formed body is elevated during electromagnetic wave drying so as to prevent cracking and other deformation of the outer wall. However, the method makes it more difficult to dry the outer peripheral part. In the case where the honeycomb formed body has a thin outer wall and partition walls and a large percent opening (i.e., poor strength of the honeycomb formed body), wrinkles and dents in the outer periphery, warpage of partition walls, and other deformation are difficult to prevent, which is problematic.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2002-283330